The present invention relates to testing devices for window grids used for resistance defrosting of windows such as is common in the auto industry. Resistance grids of this type are well-known and consist of relatively thin lines of a conducting material "painted" onto one surface of the window in a predetermined parallel grid pattern between a pair of bus lines connecting the opposing ends of each grid line.
Quality control techniques for testing the continuity of these grids are an important step in their manufacture. Prior devices developed to check for breaks in these lines have been less than satisfactory because of a lack of accuracy or a lack of proper manual manipulation of the device across the grid top assure accurate detection of any substandard grids.
With the introduction of rear window taillights, a different grid pattern is presented which adds to the difficulty of properly detecting poor quality grid lines or breaks in their continuity. Prior to the present invention, quality control testing devices have not provided the accuracy or the consistency of testing in a manner deemed fully satisfactory for the intended purpose.